1. Field of the Invention
The present invention relates to a semiconductor device having a pair of elements which are adapted to be coupled to each other in an electrically isolated state for signal transmission.
2. Description of Related Art
Devices having a transmitter element and a receiver element in pair which are adapted to be optically or magnetically coupled to each other in an electrically isolated state for signal transmission are generally referred to as isolators. Exemplary isolators are photo-couplers which include a light-emitting element such as a light-emitting diode and a light-receiving element such as a photo MOS transistor or a photo diode.
Typical constructions of the conventional photo-couplers, which are described in NIKKEI ELECTRONICS Jul. 1, 1991, pp83-92, are respectively shown in FIGS. 8 and 9. FIG. 8 illustrates a photo-coupler of opposed type in which a semiconductor chip 110 formed with a light-emitting element is opposed to a semiconductor chip 120 formed with a light-receiving element. FIG. 9 illustrates a photo-coupler of planar type in which a semiconductor chip 110 formed with a light-emitting element and a semiconductor chip 120 formed with a light-receiving element are disposed in substantially the same plane.
In either of the photo-diodes, the semiconductor chips 110, 120 are mounted on different lead frames 111, 121, and a transparent resin 101 is interposed between the semiconductor chips 110 and 120 to provide a light path therebetween. In this state, the semiconductor chips 110, 120 are encapsulated with a mold resin in a package 103, and distal edges of the lead frames 111, 121 are led out of the package 103.
In the case of the opposed type, light is transmitted through the transparent resin 101 between the opposed semiconductor chips 110 and 120, and direct light from the light-emitting element of the semiconductor chip 110 is incident on the light-receiving element of the semiconductor chip 120. In the case of the planar type, on the other hand, light emitted from the light-emitting element of the semiconductor chip 110 is reflected on an interface between the transparent resin 101 and the mold resin, and the reflected light is incident on the light-receiving element of the semiconductor chip 120.
Since the aforesaid photo-couplers are constructed such that the light-emitting element and the light-receiving element are resin-sealed with the intervention of the transparent resin 101 therebetween, size reduction thereof is difficult.
Further, the semiconductor chips 110 and 120 are respectively mounted on the different lead frames 111 and 121, so that circuits for the light-emitting element and the light-receiving element cannot be integrated. This also hinders the size reduction.
Particularly in the case of the opposed type construction, it is difficult to properly position the semiconductor chips 110 and 120 respectively mounted on the different lead frames 111 and 121. That is, the positioning of the light-emitting element with respect to the light-receiving element is difficult, so that the efficiency of the coupling between the light-emitting element and the light-receiving element is likely to be reduced.
Where an attempt is made to achieve multi-channeling by providing a plurality of light-emitting element/light-receiving element pairs in a single package in either of the aforesaid constructions, there is a difficulty in optical signal isolation between respective channels. Therefore, it is impossible to realize a multi-channel device.